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The atoi(), atol(), and atoll() functions convert the initial portion of a string token to int, long int, and long long int representation, respectively. Except for the behavior on error, they are equivalent to
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as follows:
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Unfortunately, atoi() and related functions lack a mechanism for reporting errors for invalid values. Specifically, the atoi(), atol(), and atoll() functions
- do not need to set
errnoon an error - have undefined behavior if the value of the result cannot be represented (see undefined behavior 113 of Annex J of C99)
- return 0 if the string does not represent an integer, which is indistinguishable from a correctly formatted, zero-denoting input string.
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